The present invention relates to compact and high-torque electric motors, particularly to the stator cores of externally rotating type of compact-size high-torque motors such as data-processing equipment driving motors, fan motors, or disk driving motors.
With reference to the structure of the stator in an internally rotating type of motor, the predominant conventional method of improving the coil space ratio of the motor has been by, after splitting the core into segments according to the particular number of poles, laser-welding the outer surfaces of the core segments for the fastening thereof or press-fitting or shrinkage-fitting their inner surfaces into a cylindrical housing.
For the stator of the internally rotating type of motor, however, it is difficult to fasten the core segments from the outer surface portion of the stator since the stator is constructed in such a manner that its magnetic poles are arranged radially in the direction of the outer surface of the stator from the inner surface thereof and that a magnetic gap with respect to the magnet rotor of the motor is formed on the outer surface of the stator. Besides, a member such as a housing cannot be shrinkage-fit or press-fit from the outer surface portion. For these reasons, for the stator of the internally rotating type of motor, the rotor of a coil-type direct-current motor, or the like, it has been difficult to adopt a split-core method in which the core is to be split and assembled.
Prior art relating to such split core structure of an externally rotating type of motor is described in, for example, Japanese Laid-Open Patent Publication Nos. Hei 10-94230 and Hei 11-252844.
In the case of the methods set forth in these Patent Application Publications, the stator has such structure that the yoke section and tooth section of the stator core are split, that both sections are provided with dovetail-shaped recess and protrusion, and that these dovetailed portions are combined. For both methods, however, there occur the problems that since the yoke and tooth sections are fastened only by press-fitting, the mechanical strength of the corresponding product is not sufficient, and that in view of the motor undergoing the repulsion of a torque at the end of the tooth section, the corresponding method cannot be applied to a motor of a large torque.
Also, prior art relating to structure similar to the above is set forth in Japanese Laid-Open Patent Publication No. Hei 7-203644. The method described in this Patent Application Publication relates to the structure of the rotor in an internally rotating type of motor, not the structure of the stator provided with coiling, and this motor comprises magnetic pole pieces which have the dovetail-shaped holding portion for the magnet positioned inside the rotor, and a support portion made of a non-magnetized material. For this method as well, it is obviously described that the stator core is fixed only by press-fitting and that an adhesive is not used. This method also has the problem that since the magnet undergoes centrifugal force, the motor cannot be applied to high-speed rotation, or that as with the first two methods described as examples above, this method cannot be applied to high-torque motor rotation.
Yet another example is available as a method in which, as set forth in Japanese Application Patent Laid-Open Publication No. 2000-152528, a set of connected core portions are connected. In the case of this method, the ends of teeth are connected into a small width and the cores that have been connected and linearly punched out are assembled into a circular shape after coiling, wherein one end portion finally needs to be fastened using one or another method. In this example, although the use of connection pins is described as the fastening method, other methods such as welding are also available.
In this method, however, since the section between magnetic poles is connected using a magnetized material, leakage fluxes occur between the magnetic poles and the efficiency of the motor decreases significantly. In addition, since the connected section cannot have a sufficient width for mechanical reasons, the insufficiency of mechanical strength occurs and the corresponding method is not sufficient for a high-torque motor.
Furthermore, for the internally rotating type of motor set forth in Japanese Application Patent Laid-Open Publication No. 2000-184636, the yoke section of the split core is connected by shrinkage-fitting its protruding portion and recessed portion, then punched into the recessed portion, and flared outward by plastic deformation. Consequently, the gap between the protruding portion and recessed portion is removed to form a strong and rigid connection.
Connecting the split core by plastically deforming the yoke section itself affects the magnetic characteristics of the split core, thus deteriorating the performance of the motor significantly.
As described above, no such motors of the internally rotating type or externally rotating type having the structure in which a split stator core is reassembled are seen in any products or publicly known bibliography that employ the fastened core structure capable of withstanding high-torque high-speed rotation.
In the above-described prior art, although the split core structure of the externally rotating type of motor is established for a low-torque motor, the externally rotating type of motor that has split core structure is not such that the motor can be employed in an actual product in terms of mechanical strength or long-term reliability associated with high-torque rotation. However, to achieve a coil space ratio equal to that of the internally rotating type of motor, it is desirable that even for the stator core of the externally rotating type of motor, coils should be wound around a split core. For the externally rotating type of motor, therefore, it is important to assemble a split stator core while at the same time maintaining mechanical strength equal to the core that was formed by punching split stator core segments into a single unit.
Unlike an integrated core, when a split core is assembled, individual magnetic poles can be coiled independently and this enables the improvement of a coil space ratio. In the case of an integrated core, there are the problems that since coiling is provided from slot openings, it is absolutely necessary for the slot openings to have a greater width that the conductor (coil) diameter, thus that the cogging torque of the motor must be increased to satisfy the above requirement, and hence that torque is reduced. Furthermore, the low coil space ratio of such a core increases coil resistance, permitting a greater amount of heat to occur, and resulting in deteriorated heat release performance. A split core can be adopted as one of the possible methods of solving these problems. As described above, however, the adoption of a split core poses problems associated with mechanical fastening, and these problems need to be solved.
If the method adopted for the internally rotating type of motor is applied to the externally rotating type of motor, when shrinkage-fitting is considered paradoxically, the housing is likely to be located at the inner surface portion of the core and then stressed in the direction thereof. This means that the housing is cold-shrinkage-fit, in which case, the housing to which a minus temperature difference from normal temperature has been given using liquid nitrogen or the like, is located at the inner surface portion of the core, then expands by returning to normal temperature, and stressed towards the core. With this method, however, even when the circumferentially split core is stressed in the direction of its outer surface, the stress will only spread radially and this will not enable core fastening. In addition, even when the inner surface portion is shrinkage-fit, the core itself will not be fastened since the housing will only shrink. Furthermore, shrinkage-fitting of a very thin, non-magnetized housing into the outer surface portion of the core means the spreading of a magnetic gap and deteriorates motor performance significantly.
The present invention supplies the electric motors that have a stator core formed by split core blocks in order to solve the problems described above; the fixed core having the sufficient capability to withstand the repulsion of the motor torque and not deteriorating the performance of the motor significantly.
According to the present invention, it is possible to supply a motor having a metallic connection housing which connects a plurality of split core blocks in dovetailed form to create one connected core section, wherein the motor is characterized in that the dovetailed connections at the above-mentioned connection housing are plastically deformed to remove the connection gap existing at each dovetailed connection.
In order to fulfill the above purpose, the present invention creates the structure in which the rotor core of an internally rotating type motor is split into a plurality of segments in a circumferential direction, provides each core segment with a dovetailed recess and a dovetailed protrusion at the inner surface side of the core, and further provides the housing located at the inner surface portion of the core, with the protrusion and recess that b fit into the recess and protrusion provided at the core side. The housing can be easily assembled by fitting it into a clearance, and this fitting portion has sufficient dimensions to provide the clearance required for the housing to be assembled in the fitting portion. More specifically, such dimensional relationship is established that the width of the protrusion at the housing side is smaller than the width of the recess in the fitting portion of the core, that the height of the protrusion at the housing side, of course, is also smaller than the height of the recess in the fitting portion of the core, and that the outside diameter of the housing is smaller than the inside diameter of the core. Thus, the clearance required for assembly can be obtained and the ease of assembly improves.
Provided that the above-described dimensional relationship is maintained, the gap volume of the assembling clearance is given as (Assembling clearancexc3x97Circumferential length of the fitting portionxc3x97Laminating thickness of the core). After the core and the housing have been maintained in their assembled status and the outer surface portion and laminating direction of the core have been restrained, the housing is plastically deformed from the outside of its fitting portion by use of a pressing member or a dieing tool such as a punch. In terms of volume, the amount of charging with the pressing member or die at this time is greater than the gap volume. Thus, the metal that has been charged with the die flows into the clearance between the core and the housing, and the stress required for further flow of the remainder is left as the internal residual stress of the metal. Since both the outer surface portion and laminating direction of the core are maintained in their restrained status as mentioned above, fastening between core segments and between the housing and the core is established by the residual stress applied between the housing and the core. At this time, since the mechanical gaps between adjacent core segments are eliminated, magnetic connection is established and improved motor characteristics are anticipated.
Furthermore, the laminating direction of the core can also be fixed at the same time according to the particular manner of giving plastic deformation, in other words, the shape of the dieing tool, such as punch, that is to be inserted. That is to say, the laminating direction of the core can be fixed by giving a stepped shape to the punch to be inserted into the fitting portion and spreading the edge of the housing.
The fact that above-mentioned fastening is possible means that the assembly structure of the split core can be established and that the shape of the core increases in the degree of freedom. The diameter of the slot openings described earlier in this document can be reduced, regardless of the conductor coiling diameter, and the coil space ratio can also be improved. Also, since the space ratio can be improved, coil resistance can be reduced, and in addition, since the thermal conductivity between conductors improves, the temperature characteristics of the motor can be improved. Hence, critical motor designing becomes possible and this, in turn, enables size reduction and the improvement of efficiency. At this time, since the magnetic flux density created by the coils improves, there also arise the disadvantages that magnetic saturation occurs at the ends of the teeth and that the rotor magnet becomes demagnetized. The high degree of freedom in the design of the core shape, however, enables the improvement of disadvantages not brought about by the prior art.